Aviation safety investigators explain Rolls-Royce engine failure

ATSB recites sequence of events that led up to Trent 900 engine explosion

The Australian Transport Safety Bureau (ATSB) has put forward what it believes was the sequence of events that led to the failure of a Rolls-Royce Trent 900 engine on a Qantas A380 superjumbo in November.

The ATSB’s safety report said that the No 2 engine had sustained an uncontained failure of the intermediate-pressure (IP) turbine disc. Sections of the liberated disc had penetrated the left wing and the left wing-to-fuselage fairing, resulting in structural and systems damage to the aircraft. The No 2 engine was removed from the aircraft and disassembled in an authorised engine workshop for examination. In addition, a large section of IP turbine disc was also recovered from Batam Island in Indonesia for examination. Those examinations are ongoing.

Recent examination of components removed from the failed engine at Rolls-Royce in Derby identified the presence of fatigue cracking within a stub pipe that feeds oil into the high pressure/intermediate pressure bearing structure. While the analysis of the engine failure is ongoing, it has been identified that the leakage of oil into the HP/IP bearing structure buffer space (and a subsequent oil fire within that area) was central to the engine failure and IP turbine disc liberation event.

Further examination of the cracked area has identified the axial misalignment of an area of counterboring within the inner diameter of the stub pipe; the misalignment having produced a localised thinning of the pipe wall on one side. Misaligned stub pipe counter-boring is understood to be related to the manufacturing process. This condition could lead to an elevated risk of fatigue crack initiation and growth, oil leakage and potential catastrophic engine failure from a resulting oil fire, said ATSB.

The ATSB said that it had recommended that Rolls-Royce address the safety issue and take actions necessary to ensure the safety of flight operations in aircraft equipped with Rolls-Royce Trent 900 series engines. Martin Dolan, the ATSB’s chief commissioner, said: “We stress that this is a preliminary report. It is intended to set out the sequence of events as we understand it so far and to highlight the safety issue we have identified. A comprehensive report will be completed within a year of the occurrence.”